minor fix


git-svn-id: svn://svn.code.sf.net/p/fonttools/code/trunk@118 4cde692c-a291-49d1-8350-778aa11640f8
diff --git a/Lib/fontTools/ttLib/sfnt.py b/Lib/fontTools/ttLib/sfnt.py
index 2fdeb99..4a4a7e7 100644
--- a/Lib/fontTools/ttLib/sfnt.py
+++ b/Lib/fontTools/ttLib/sfnt.py
@@ -213,7 +213,7 @@
 	while x:
 		x = x >> 1
 		exponent = exponent + 1
-	return exponent - 1
+	return max(exponent - 1, 0)
 
 
 def getsearchrange(n):